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Black carbon (BC) particles in the Arctic contribute to rapid warming of the Arctic by heating the atmosphere and snow and ice surfaces. Understanding the source contributions to Arctic BC is therefore important, but they are not well understood, especially those for atmospheric and snow radiative effects. Here we estimate simultaneously the source contributions of Arctic BC to near-surface and vertically integrated atmospheric BC mass concentrations (MBC_SRF and MBC_COL), BC deposition flux (MBC_DEP), and BC radiative effects at the top of the atmosphere and snow surface (REBC_TOA and REBC_SNOW), and show that the source contributions to these five variables are highly different. In our estimates, Siberia makes the largest contribution to MBC_SRF, MBC_DEP, and REBC_SNOW in the Arctic (defined as > 70° N), accounting for 70 %, 53 %, and 43 %, respectively. In contrast, Asia’s contributions to MBC_COL and REBC_TOA are largest, accounting for 38 % and 45 %, respectively. In addition, the contributions of biomass burning sources are larger (24−34 %) to MBC_DEP, REBC_TOA, and REBC_SNOW, which are highest from late spring to summer, and smaller (4.2−14 %) to MBC_SRF and MBC_COL, whose concentrations are highest from winter to spring. These differences in source contributions to these five variables are due to seasonal variations in BC emission, transport, and removal processes and solar radiation, as well as to differences in radiative effect efficiency (radiative effect per unit BC mass) among sources. Radiative effect efficiency varies by a factor of up to 4 among sources (1465−5439 W g–1) depending on lifetimes, mixing states, and heights of BC and seasonal variations of emissions and solar radiation. As a result, source contributions to radiative effects and mass concentrations (i.e., REBC_TOA and MBC_COL, respectively) are substantially different. The results of this study demonstrate the importance of considering differences in the source contributions of Arctic BC among mass concentrations, deposition, and atmospheric and snow radiative effects for accurate understanding of Arctic BC and its climate impacts.

The Arctic region is sensitive to climate change and is warming faster than the global average. Aerosol particles change cloud properties by acting as cloud condensation nuclei and ice-nucleating particles, thus influencing the Arctic climate system. Therefore, understanding the aerosol particle properties in the Arctic is needed to interpret and simulate their influences on climate. In this study, we collected ambient aerosol particles using whole-air and PM10 inlets and residual particles of cloud droplets and ice crystals from Arctic low-level clouds (typically, all-liquid or mixed-phase clouds) using a counterflow virtual impactor inlet at the Zeppelin Observatory near Ny-Ålesund, Svalbard, within a time frame of 4 years. We measured the composition and mixing state of individual fine-mode particles in 239 samples using transmission electron microscopy. On the basis of their composition, the aerosol and cloud residual particles were classified as mineral dust, sea salt, K-bearing, sulfate, and carbonaceous particles. The number fraction of aerosol particles showed seasonal changes, with sulfate dominating in summer and sea salt increasing in winter. There was no measurable difference in the fractions between ambient aerosol and cloud residual particles collected at ambient temperatures above 0 ∘C. On the other hand, cloud residual samples collected at ambient temperatures below 0 ∘C had several times more sea salt and mineral dust particles and fewer sulfates than ambient aerosol samples, suggesting that sea spray and mineral dust particles may influence the formation of cloud particles in Arctic mixed-phase clouds. We also found that 43 % of mineral dust particles from cloud residual samples were mixed with sea salt, whereas only 18 % of mineral dust particles in ambient aerosol samples were mixed with sea salt. This study highlights the variety in aerosol compositions and mixing states that influence or are influenced by aerosol–cloud interactions in Arctic low-level clouds.

During the PAMARCMiP 2018 campaign (March and April 2018) a proton-transfer-reaction mass spectrometer (PTR-MS) was deployed onboard the POLAR 5 research aircraft and sampled the High Arctic atmosphere under Arctic haze conditions. More than 100 compounds exhibited levels above 1 pmol/mol in at least 25% of the measurements. We used back trajectories and acetone mixing ratios to identify periods with and without long-range transport from continental sources.Air masses with continental influence contained elevated levels of compounds associated with (aged) biogenic emissions or aged anthropogenic pollution (e.g., methanol, peroxyacetylnitrate (PAN), acetone, acetic acid, methylethylketone (MEK), proprionic acid, and pentanone), but benzene – a marker for primary pollution – was not enhanced. Almost half of all positively detected compounds (>100) in the High Arctic atmosphere can be associated with terpene oxidation products. This constitutes a strong signature of biogenic terpenes and their oxidation products on the High Arctic atmosphere. Many of these compounds will condense and produce biogenic secondary organic aerosol (SOA) – a natural source of organic aerosol (OA) in addition to the aerosols that can be associated with anthropogenic pollution. Therefore, we hypothesize that biogenic SOA exerted significant control over the complex system of aerosols, clouds and longwave radiation in the pre-industrial Arctic winter, even though their role is likely marginal under contemporary polluted Arctic haze conditions. However, biogenic SOA may become an important factor in the future again, if biogenic emissions are enhanced due to climate change and if polluting technologies are (hopefully) phased out in the near future.During two flights, surface ozone depletion events (ODE) were observed that coincided with enhanced levels of acetone, and methylethylketone. There is evidence that ODEs may also be associated with the emission of biogenic ice-nucleating particles (INP) because the filter samples taken during these two flights exhibited enhanced levels of highly active ice-nucleating particles (INP).Both these processes, INP production in association with ozone depletion events, and the transport of biogenic SOA could require corrections in estimates of preindustrial radiative forcing (RF). If preindustrial RF has been stronger, the Arctic amplification would be even stronger than currently assumed.

Long-term measurements of black carbon (BC) are warranted for investigating changes in its emission, transport, and deposition. However, depending on instrumentation, parameters related to BC such as aerosol absorption coefficient (babs) have been measured instead. Most ground-based measurements of babs in the Arctic have been made by filter-based absorption photometers, including multi-angle absorption photometers (MAAP), particle soot absorption photometers (PSAP), continuous light absorption photometer (CLAP), and Aethalometers. The measured babs can be converted to atmospheric mass concentrations of BC (MBC) by assuming the value of the mass absorption cross section (MAC = babs/MBC). However, the accuracy of conversion of babs to MBC has not been adequately assessed. Here, we introduce a systematic method for deriving MAC values from babs measured by these instruments and independently measured MBC. In this method, MBC was measured with a filter-based absorption photometer with a heated inlet (COSMOS). COSMOS-derived MBC (MBC (COSMOS)) is traceable to a rigorously calibrated single particle soot photometer (SP2) and the absolute accuracy of MBC (COSMOS) has been demonstrated previously to be about 15 % in Asia and the Arctic. The necessary conditions for application of this method are a high correlation of the measured babs with independently measured MBC, and long-term stability of the correlation slope, which represents the MAC. In general, babs – MBC (COSMOS) correlations were high (r2 = 0.84–0.96 for hourly data) at Fukue in Japan, Barrow in Alaska, Ny-Ålesund in Svalbard, Pallastunturi in Finland, and Alert in Canada, and stable up to for 10 years. We successfully estimated MAC values (11.0–15.2 m2 g−1 at a wavelength of 550 nm) for these instruments and these MAC values can be used to obtain error-constrained estimates of MBC from babs measured at these sites even in the past, when COSMOS measurements were not made. Because the absolute values of MBC in these Arctic sites estimated by this method are consistent with each other, they are applicable to study spatial and temporal variation of MBC and to evaluate performance of numerical model calculations.

To constrain uncertainties in radiative forcings associated with aerosol--cloud interactions, improved understanding of Arctic cloud formation is required, yet long-term measurements of the relevant cloud and aerosol properties remain sparse. We present the first long-term study of cloud residuals, i.e. particles that were involved in cloud formation, and ambient aerosol particles in Arctic low-level clouds measured at Zeppelin Observatory, Svalbard. A detailed evaluation of the ground-based counter-flow virtual impactor inlet system is also presented. Cloud residuals as small as 15 nm are routinely observed especially during the dark period and are potentially linked to ice, supporting prior work suggesting that classical droplet activation is not the only relevant process in the formation of Arctic low-level clouds. The reported measurements and findings provide a new basis for improving our understanding of Arctic clouds and for developing robust parameterisations of mixed-phase clouds in Earth system models.

Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimations of aerosol direct and indirect effects. In this study, we develop an aerosol module, designated the Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can explicitly represent these parameters by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 μm to resolve both aerosol sizes (12 bins) and BC mixing states (10 bins) for a total of 120 bins. The particles with diameters between 1 and 40 nm are resolved using additional eight size bins to calculate NPF. The ATRAS module is implemented in the WRF-Chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging, and SOA processes over East Asia during the spring of 2009. The BC absorption enhancement by coating materials is about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement is estimated to be 10–20% over northern East Asia and 20–35% over southern East Asia. A clear north–south contrast is also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increases CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increases CCN concentrations at lower supersaturations (larger particles) over southern East Asia. The application of ATRAS in East Asia also shows that the impact of each process on each optical and radiative parameter depends strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under different meteorological conditions and emissions.